1. Field of the Invention
The present invention relates to the novel tartaric acid ether compounds useful as pharmaceuticals, functional foods and the like. More particularly, it relates to a novel enzyme producing tartaric acid ether compound which catalyzes a reaction of producing a tartaric acid ether compound in which the phenolic hydroxyl group(s) of flavonoids or the analogous compounds having phenolic hydroxyl group(s) is acted to an epoxy ring of an epoxysuccinic acid to form an ether linkage, an enzymatic process for producing the tartaric acid ether compounds using the said enzyme, and the novel tartaric acid ether compounds.
2. Description of the Related Prior Art
It is known that 2-hydroxy-3-[[3-(4-hydroxyphenyl)-4-oxo-4H-1-benzopyran-7-yl]oxy]-butanedi oic acid (see "Isoflavone derivative peak A" in JP-A-9-110857), 2-hydroxy-3-[[5-hydroxy-3-(4-hydroxyphenyl)-4-oxo-4H-1-benzopyran-7-yl]oxy ]-butanedioic acid (see "Isoflavone derivative peak B" in JP-A-9-110857) and 2-[[5,8-dihydroxy-3-(4-hydroxyphenyl)-4-oxo-4H-1-benzopyran-7-yl]oxy]-3-hy droxy-butanedioic acid (see "Isoflavone derivative peak A" in JP-A-10-59956), which are the tartaric acid ether compounds and the isoflavone derivatives, show a prominent inhibitory action against histidine decarboxylase (HDC) which takes part in the biosynthesis of histamine causative of ulcers and allergic diseases, and thus are very useful for the preparation of pharmaceuticals and functional foods free from harmful side effects.
Hitherto, despite their manifold physiological activities such as antioxidant action, HDC inhibitory action, estrogen-like action and anti-ulcer action, many of the flavonoids or their analogous compounds have fallen short of exhibiting their potential efficacy in the living body, just because of their low solubility in water.
The glycosides of flavonoids or their analogues show high solubility in water but are unstable in their structure. In contrast, the tartaric acid ether compounds of flavonoids or their analogues are very stable structurally.
In view of the above, it is significantly important to provide the tartaric acid ether compounds with high water solubility and stable structure, for example, the tartaric acid ether compounds of flavonoids and their analogues. Hitherto, various methods, such as synthesis through substitution reaction, synthesis through addition reaction, synthesis through leaving reaction or condensation reaction, synthesis through oxidation reaction and synthesis through reduction reaction, have been proposed and used for producing the ether compounds, but any of these methods has recourse to a chemical reaction and involves complicate operations and steps in connection with the reaction conditions and reaction reagents, and also requires specific synthesizing equipment. On the other hand, these has not entirely been known the technique for producing the tartaric acid ether compounds at low cost and with ease according to the enzyme process.